Molybdenum carbide

ABSTRACT

Molybdenum carbide (MoC and Mo 2 C) produced by heating a precursor material in a first heating zone to a first temperature in the presence of a reducing gas and a carbonizing gas and moving the precursor material to a second heating zone that is heated to a second temperature that is at least 100° C. hotter than the first heating zone to form said molybdenum carbide.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a divisional of co-pending U.S. patent application Ser.No. 10/007,349, filed on Nov. 7, 2001, now allowed, which is herebyincorporated herein by reference for all that it discloses.

TECHNICAL FIELD

[0002] The invention generally pertains to molybdenum carbides, and morespecifically, to production of molybdenum carbide.

BACKGROUND

[0003] Hydrogen reacts with oxygen to generate energy while producingwater instead of the pollutants typically associated with the combustionof fossil fuels. Therefore, hydrogen is potentially a significant sourceof “clean” energy. Among other uses, hydrogen is also used on anindustrial basis for chemical synthesis (e.g., methanol and ammoniasynthesis).

[0004] Sources of hydrogen include methane, a significant component ofrelatively abundant natural gas. Processes such as steam reforming anddry reforming of methane may be used to produce hydrogen gas and carbonmonoxide. However, the catalysts required for these reactions aretypically made of expensive noble metals, such as elemental gold,platinum, iridium, ruthenium, and nickel. In addition, these catalystsmust be replaced frequently as they tend to become plugged andeventually deactivated by carbon deposits. Molybdenum carbides (MoCand/or Mo₂C) have been shown to be a viable and less expensivealternative to noble metal catalysts for a variety of reactions,including oxidation of methane to form hydrogen gas.

[0005] Various processes have been developed for producing molybdenumcarbide. According to one such process for producing Mo₂C, ammoniummolybdate powder is loaded into a quartz liner and placed into a rotarykiln. The system is first purged with nitrogen, then a hydrogen andcarbon monoxide mixture is introduced. Initially, the temperature is setto 300° C. to decompose the ammonium molybdate. Thereafter, thetemperature may only be ramped between 2° C. and 20° C. per minute. TheMo₂C forms during a three to five hour soak at a temperature between550° C. and 600° C. The reactor is then cooled, and the Mo₂C powder maybe passivated with diluted oxygen or air after the powder cools to roomtemperature.

[0006] However, this process for producing molybdenum carbide requiresthe temperature ramp rate not exceed 20° C. per minute, and is thus atime-consuming process. In addition, this is a batch process, whichslows production and increases production costs.

SUMMARY

[0007] MoC produced by heating a precursor material in a first heatingzone to a first temperature in the presence of a reducing gas and acarbonizing gas and moving the precursor material to a second heatingzone that is heated to a second temperature that is at least 100° C.hotter than the first heating zone.

[0008] Mo₂C produced by heating a precursor material in a first heatingzone to a first temperature in the presence of a reducing gas and acarbonizing gas and moving the precursor material to a second heatingzone that is heated to a second temperature that is at least 100° C.hotter than the first heating zone.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Illustrative and presently preferred embodiments of the inventionare illustrated in the drawings, in which:

[0010]FIG. 1 is a cross-sectional schematic representation of oneembodiment of apparatus for producing molybdenum carbide according tothe invention;

[0011]FIG. 2 is a cross-sectional view of three sections of a processchamber illustrating molybdenum carbide production; and

[0012]FIG. 3 is a flow chart illustrating an embodiment of a method forproducing molybdenum carbide according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] Apparatus 10 (FIG. 1) is shown and described herein as it may beused to produce molybdenum carbide 12. Briefly, molybdenum carbides (MoCand/or Mo₂C) offer a viable and less expensive alternative to noblemetal catalysts for a variety of reactions, including the production ofhydrogen. Although various processes have been developed for producingmolybdenum carbides, these tend to be non-continuous and slow. Forexample, one batch process for producing Mo₂C requires the temperatureramp rate not exceed 20° C. per minute. Instead, it is desirable toproduce molybdenum carbide on a continuous, and hence cost-effectivebasis, particularly for industrial or commercial applications.

[0014] According to the teachings of the invention, embodiments ofapparatus 10 for producing molybdenum carbide 12 are disclosed.Apparatus 10 may comprise a process gas 62, and a process chamber 34.The precursor material 14 (e.g., MoO₃) and the process gas 62 (e.g., amixture of hydrogen and carbon monoxide gasses) are received in theprocess chamber 34. For example, for MoC production, the process chamber34 may comprise heating zones 20, 21, and 22, wherein the first heatingzone 20 is heated to about 555° C., and the second and third heatingzones 21 and 22 are each heated to about 900° C. Or for example, forMo₂C production, the process chamber 34 may comprise heating zones 20,21, and 22, wherein the first heating zone 20 is heated to about 555°C., the second heating zone 21 is heated to about 800° C., and the thirdheating zone 22 is heated to about 1000° C. In any event, the precursormaterial 14 reacts with the process gas 62 within the process chamber 34to form molybdenum carbide product 12.

[0015] Apparatus 10 may be operated as follows for producing molybdenumcarbide 12 from a precursor material 14 (e.g., molybdic oxide (MoO₃)).As one step in the process, the precursor material is heated in a firsttemperature zone (e.g., in Heating Zone 1 of furnace 16) in the presenceof a reducing gas 64 and a carbonizing gas 63. Thereafter, the precursormaterial is moved to a second heating zone (e.g., in Heating Zone 2)that is at a temperature at least 100° C. greater than the first heatingzone to form the molybdenum carbide product 12.

[0016] Accordingly, the apparatus and method may be used to produce MoCand Mo₂C in a continuous manner. Preferably, no intermediate handling isrequired during production of the molybdenum carbide product 12. Thatis, the precursor material 14 is preferably fed into a product inlet end15 of furnace 16, and the molybdenum carbide product 12 is removed froma product discharge end 17 of furnace 16, allowing the molybdenumcarbide to be produced in about three hours. As such, production ofmolybdenum carbide 12 according to embodiments of the invention is lesslabor intensive, less time consuming, and production costs may be lowerthan conventional processes for producing molybdenum carbide.

[0017] Having generally described apparatus and methods for productionof molybdenum carbide, as well as some of the more significant featuresand advantages of the invention, the various embodiments of theinvention will now be described in further detail.

APPARATUS FOR PRODUCING MOLYBDENUM CARBIDE

[0018] An embodiment of apparatus 10 for producing molybdenum carbide 12(i.e., MoC and/or Mo₂C) according to embodiments of the invention isshown in FIG. 1. As an overview, the apparatus 10 may generally comprisea furnace 16, a transfer system 32, and a process gas 62, each of whichwill be explained in further detail below. The transfer system 32 may beused to introduce a precursor material 14 into the furnace 16 and moveit through the furnace 16, for example, in the direction illustrated byarrow 26. In addition, the process gas 62 may be introduced into thefurnace 16, for example, in the direction illustrated by arrow 28.Accordingly, the process gas 62 reacts with the precursor material 14 inthe furnace 16 to form molybdenum carbide product 12, as explained inmore detail below with respect to embodiments of the method of theinvention.

[0019] A preferred embodiment of apparatus 10 is shown in FIG. 1 anddescribed with respect thereto. Apparatus 10 preferably comprises arotating tube furnace 16. Accordingly, the transfer system 32 maycomprise at least a process chamber 34 extending through three heatingzones 20, 21, and 22 of the furnace 16, and through a cooling zone 23.In addition, the transfer system 32 may also comprise a feed system 36for feeding the precursor material 14 into the process chamber 34, and adischarge hopper 38 at the far end of the process chamber 34 forcollecting the molybdenum carbide product 12 that is produced in theprocess chamber 34.

[0020] Before beginning a more detailed description of preferredembodiments of apparatus 10, however, it should be clear that otherembodiments of the furnace 16 and the transfer system 32 arecontemplated as being within the scope of the invention. The furnace maycomprise any suitable furnace or design thereof, and is not limited tothe rotating tube furnace 16, shown in FIG. 1 and described in moredetail below. For example, according to other embodiments of theinvention, the furnace 16 may also comprise, but is not limited to, morethan one distinct furnace (e.g., instead of the single furnace 16 havingseparate heating zones 20, 21, 22 that are defined by refractory dams 46and 47). Likewise, the transfer system 32, shown in FIG. 1 and describedin more detail below, may comprise a variety of other means forintroducing the precursor material 14 into the furnace 16, for movingthe precursor material 14 through the furnace 16, and/or for collectingthe molybdenum carbide product 12 from the furnace 16. For example, inother embodiments the transfer system 32 may comprise manualintroduction (not shown) of the precursor material 14 into the furnace16, a conveyor belt (not shown) for moving the precursor material 14through the furnace 16, and/or a mechanical collection arm (not shown)for removing the molybdenum carbide product 12 from the furnace 16.Other embodiments of the furnace 16, and the transfer system 32, nowknown or later developed, are also contemplated as being within thescope of the invention, as will become readily apparent from thefollowing detailed description of preferred embodiments of apparatus 10.

[0021] Turning now to a detailed description of preferred embodiments ofapparatus 10, a feed system 36 may be operatively associated with theprocess chamber 34. The feed system 36 may continuously introduce theprecursor material 14 into the furnace 16. In addition, the feed system36 may also introduce the precursor material 14 into the furnace 16 at aconstant rate. For example, the feed system 36 may comprise aloss-in-weight feed system for continuously introducing the precursormaterial 14 into one end of the process chamber 34 at a constant rate.

[0022] It is understood that according to other embodiments of theinvention, the precursor material 14 may be otherwise introduced intothe furnace 16. For example, the feed system 36 may feed the precursormaterial 14 into the furnace 16 on an intermittent basis or in batch.Other designs for the feed system 36 are also contemplated as beingwithin the scope of the invention and may differ depending upon designconsiderations and process parameters, such as the desired rate ofproduction of the molybdenum carbide product 12.

[0023] In any event, the precursor material 14 is preferably introducedinto the furnace 16 by feeding it into the process chamber 34. Theprocess chamber 34 preferably extends through a chamber 44 that isformed within the furnace 16. The process chamber 34 may be positionedwithin the chamber 44 so as to extend substantially through each of theheating zones 20, 21, and 22 of the furnace 16. Preferably, the processchamber 34 extends in approximately equal portions through each of theheating zones 20, 21, and 22 although this is not required. In addition,the process chamber 34 may further extend beyond the heating zones 20,21, and 22 of the furnace 16 and through a cooling zone 23.

[0024] According to preferred embodiments of the invention, the processchamber 34 is a gas-tight, high temperature (HT) alloy process chamber.The process chamber 34 also preferably has a nominal external diameterof about 16.5 centimeters (cm) (about 6.5 inches (in)), a nominalinternal diameter of about 15.2 cm (about 6 in), and is about 305 cm(about 120 in) long. Preferably, about 50.8 cm (about 20 in) segments ofthe process chamber 34 each extend through each of the three heatingzones 20, 21, and 22 of the furnace 16, and the remaining approximately152.4 cm (60 in) of the process chamber 34 extend through the coolingzone 23.

[0025] In other embodiments of the invention, however, the processchamber 34 may be manufactured from any suitable material. In addition,the process chamber 34 need not extend equally through each of theheating zones 20, 21, and 22 and/or the cooling zone 23. Likewise, theprocess chamber 34 may be any suitable length and diameter. The precisedesign of the process chamber 34 will depend instead on designconsiderations, such as the feed rate of the precursor material 14, thedesired production rate of the molybdenum carbide product 12, thetemperature for each heating zone 20, 21, and 22, among other designconsiderations readily apparent to one skilled in the art based on theteachings of the invention.

[0026] The process chamber 34 is preferably rotated within the chamber44 of the furnace 16. For example, the transfer system 32 may comprise asuitable drive assembly operatively associated with the process chamber34. The drive assembly may be operated to rotate the process chamber 34in either a clockwise or counter-clockwise direction, as illustrated byarrow 42 in FIG. 1. Preferably, the process chamber 34 is rotated at aconstant rate. The rate is preferably selected from the range ofapproximately 18 to 100 seconds per revolution. For example, the processchamber 34 may be rotated at a constant rate of 18 seconds perrevolution. However, the process chamber 34 may be rotated faster,slower and/or at variable rotational speeds, as required depending ondesign considerations, desired product size, and the set points of otherprocess variables as would be apparent to persons having ordinary skillin the art after having become familiar with the teachings of theinvention.

[0027] The rotation 42 of the process chamber 34 may facilitate movementof the precursor material 14 and the intermediate material 30 (FIG. 2)through the heating zones 20, 21, and 22 of the furnace 16, and throughthe cooling zone 23. In addition, the rotation 42 of the process chamber34 may facilitate mixing of the precursor material 14 and theintermediate material 30. As such, the unreacted portion of theprecursor material 14 and the intermediate material 30 is continuouslyexposed for contact with the process gas 62. Thus, the mixing mayfurther enhance the reaction between the precursor material 14 and theintermediate material 30 and the process gas 62.

[0028] In addition, the process chamber 34 is preferably positioned atan incline 40 within the chamber 44 of the furnace 16. One embodimentfor inclining the process chamber 34 is illustrated in FIG. 1. Accordingto this embodiment of the invention, the process chamber 34 may beassembled on a platform 55, and the platform 55 may be hinged to a base56 so that the platform 55 may pivot about an axis 54. A lift assembly58 may also engage the platform 55. The lift assembly 58 may be operatedto raise or lower one end of the platform 55 with respect to the base56. As the platform 55 is raised or lowered, the platform 55 rotates orpivots about the axis 54. Accordingly, the platform 55, and hence theprocess chamber 34, may be adjusted to the desired incline 40 withrespect to the grade 60.

[0029] Although preferred embodiments for adjusting the incline 40 ofthe process chamber 34 are shown and described herein with respect toapparatus 10 in FIG. 1, it is understood that the process chamber 34 maybe adjusted to the desired incline 40 according to any suitable manner.For example, the process chamber 34 may be fixed at the desired incline40 and thus need not be adjustably inclined. As another example, theprocess chamber 34 may be inclined independently of the furnace 16,and/or the other components of apparatus 10 (e.g., feed system 36).Other embodiments for inclining the process chamber 34 are alsocontemplated as being within the scope of the invention, and will becomereadily apparent to one skilled in the art based upon an understandingof the invention.

[0030] In any event, the incline 40 of the process chamber 34 may alsofacilitate movement of the precursor material 14 and intermediatematerial 30 through the heating zones 20, 21, and 22 of the furnace 16,and through the cooling zone 23. In addition, the incline 40 of theprocess chamber 34 may facilitate mixing of the precursor material 14and intermediate material 30 within the process chamber 34, and exposethe same for contact with the process gas 62 to enhance the reactionsbetween the precursor material 14 and/or the intermediate material 30and the process gas 62. Indeed, the combination of the rotation 42 andthe incline 40 of the process chamber 34 may further enhance thereactions for forming molybdenum carbide product 12.

[0031] As previously discussed, the furnace 16 preferably comprises achamber 44 formed therein. The chamber 44 defines a number of controlledtemperature zones surrounding the process chamber 34 within the furnace16. In one embodiment, three temperature zones 20, 21, and 22 aredefined by refractory dams 46 and 47. The refractory dams 46 and 47 arepreferably closely spaced to the process chamber 34 so as to discouragethe formation of convection currents between the temperature zones. Inone embodiment, for example, the refractory dams 46 and 47 come towithin approximately 1.3 to 1.9 cm (0.5 to 0.75 in) from the processchamber 34 to define three heating zones 20, 21, and 22 in the furnace16. In any event, each of the three heating zones is preferablyrespectively maintained at the desired temperatures within the chamber44 of the furnace 16. And hence, each segment of the process chamber 34is also maintained at the desired temperature, as shown in more detailin FIG. 2 discussed below.

[0032] Preferably, the chamber 44 of the furnace 16 defines the threeheating zones 20, 21, and 22 shown and described herein with respect toFIG. 1. Accordingly, the precursor material 14 may be subjected todifferent reaction temperatures as it is moved through each of theheating zones 20, 21, and 22 in the process chamber 34. That is, as theprecursor material 14 is moved through the process chamber 34 and intothe first heating zone 20, the precursor material 14 is subjected to thetemperature maintained within the first heating zone. Likewise, as theprecursor material 14 is moved through the process chamber 34 from thefirst heating zone 20 and into the second heating zone 21, it issubjected to the temperature maintained within the second heating zone.

[0033] It is understood that the heating zones 20, 21, and 22 may bedefined in any suitable manner. For example, the heating zones 20, 21,and 22 may be defined by baffles (not shown), by a number of separatechambers (not shown), etc. Indeed, the heating zones 20, 21, and 22 neednot necessarily be defined by refractory dams 46, 47, or the like. As anexample, the process chamber 34 may extend through separate, consecutivefurnaces (not shown). As another example, the chamber 44 of the furnace16 may be open and a temperature gradient may be generated within thechamber 44 to extend from one end of the chamber 44 to the opposite endof the chamber 44 using separate heating elements spaced along thelength thereof.

[0034] It is also understood that more than three heating zones (notshown) may be defined within the furnace 16. According to yet otherembodiments of the invention, fewer than three heating zones (also notshown) may be defined in the furnace 16. For example, according to oneembodiment of the method of the invention, discussed in more detailbelow, the temperature of Heating Zone 2 (21) and Heating Zone 3 (22)are approximately the same. In such an embodiment, these heating zonesmay be combined into a single heating zone (e.g., by removing therefractory dam 47 therebetween). Still other embodiments will occur tothose skilled in the art based on the teachings of the invention and arealso contemplated as being within the scope of the invention.

[0035] The furnace 16 may be maintained at the desired temperaturesusing suitable temperature control means. In preferred embodiments, eachof the heating zones 20, 21, and 22 of the furnace 16 are respectivelymaintained at the desired temperatures using suitable heat sources,temperature control, and over-temperature protection. For example, theheat source may comprise independently controlled heating elements 50,51, and 52 positioned within each of the heating zones 20, 21, and 22 ofthe furnace 16, and linked to suitable control circuitry.

[0036] In one preferred embodiment, the temperature is regulated withinthe three heating zones 20, 21, and 22 of the furnace 16 by twenty-eightsilicon-carbide, electrical-resistance heating elements. The heatingelements are linked to three Honeywell UDC3000 MicroprocessorTemperature Controllers (i.e., one controller for each of the threeheating zones 20, 21, and 22) for setting and controlling thetemperature thereof. In addition, three Honeywell UDC2000 MicroprocessorTemperature Limiters (i.e., also one controller for each of the threeheating zones 20, 21, and 22) are provided for over-temperatureprotection. It is understood, however, that any suitable temperatureregulating means may be used to set and maintain the desired temperaturewithin the furnace 16. For example, the heating elements need notnecessarily be electronically controlled and may instead be manuallycontrolled.

[0037] Although each of the heating zones are preferably maintained atrelatively uniform temperatures, respectively, it is apparent thatconduction and convection of heat may cause a temperature gradient to beestablished within one or more of the heating zones 20, 21, and 22. Forexample, although the refractory dams 46, 47 are spaced approximately1.3 to 1.9 cm (0.5 to 0.75 in) from the process chamber 34 to reduce orminimize the transfer or exchange of heat between the heating zones 20,21, and 22, some heat exchange may still occur therebetween. Also forexample, the process chamber 34 and/or the precursor material and/orintermediate material may also conduct heat between the heating zones20, 21, and 22. Therefore, the temperature measured at various pointswithin each of the heating zones 20, 21, and 22 may be several degreescooler or several degrees warmer (e.g., by about 50 to 100° C.) than thecenter of the heating zones 20, 21, and 22. Other designs are alsocontemplated to further reduce the occurrence of these temperaturegradients, such as sealing the refractory dams 46, 47 about the processchamber 34. In any event, the temperature settings for each of theheating zones 20, 21, and 22 are preferably measured in the center ofeach of the heating zones 20, 21, and 22 to more accurately maintain thedesired temperature therein.

[0038] Preferably, the cooling zone (illustrated by outline 23 inFIG. 1) comprises a portion of the process chamber 34 that is open tothe atmosphere. Accordingly, the molybdenum carbide product 12 isallowed to cool prior to being collected in the collection hopper 38.However, according to other embodiments of the invention, the coolingzone 23 may be one or more enclosed portions of apparatus 10. Likewise,suitable temperature regulating means may be used to set and maintainthe desired temperature within the enclosed cooling zone 23. Forexample, a radiator may circulate fluid about the process chamber 34 incooling zone 23. Or for example, a fan or blower may circulate a coolinggas about the process chamber 34 in cooling zone 23.

[0039] The process gas 62 is preferably introduced into the furnace 16for reaction with the precursor material 14 and the intermediate product30. According to preferred embodiments of the invention, the process gas62 may comprise a carbonizing gas 63 and a reducing gas 64. Alsoaccording to preferred embodiments, an inert gas 65 may be provided forpurging the process chamber 34 before beginning the process (e.g., toremove any oxygen or other contaminants from the process chamber 34),and/or after finishing the process (e.g., for safety reasons such asremoving any flammable gasses).

[0040] It is understood that the carbonizing gas 63, the reducing gas64, and the inert gas 65 may be stored in separate gas cylinders nearthe far end of the process chamber 34, as shown in FIG. 1. Individualgas lines, also shown in FIG. 1, may lead from the separate gascylinders to a gas inlet 25 at the far end of the process chamber 34. Asuitable gas regulator (not shown) may be provided to introduce thecarbonizing gas 63, the reducing gas 64, and the inert gas 65 from therespective gas cylinders into the process chamber 34 in the desiredproportions, at the desired timing, and at the desired rate. However, inother embodiments, some or all of the gasses may be “premixed” andprovided in one or more cylinders for delivery to the process chamber34.

[0041] According to embodiments of the invention, the carbonizing gas 63may be carbon monoxide gas, the reducing gas 64 may be hydrogen gas, andthe inert gas 65 may be argon or nitrogen gas. However, it is understoodthat any suitable carbonizing gas 63, reducing gas 64, inert gas 65, ormixture thereof, may be used according to the teachings of theinvention. For example, in other embodiments, the process gas 62 mayinstead comprise methane gas instead of separate reducing andcarbonizing gasses. The composition of the process gas 62 will depend ondesign considerations, such as the cost and availability of the gases,safety issues, and the desired rate of production, among otherconsiderations.

[0042] Preferably, the process gas 62 is introduced into the processchamber 34 and directed through the cooling zone 23 and through each ofthe heating zones 20, 21, and 22, in a direction opposite (i.e.,counter-current, as illustrated by arrow 28) to the direction 26 thatthe precursor material 14 is moved through each of the heating zones 20,21, and 22 of the furnace 16, and through the cooling zone 23. Directingthe process gas 62 through the furnace 16 in a direction that isopposite or counter-current 28 to the direction 26 that the precursormaterial 14 is moving through the furnace 16 may increase the rate ofthe reaction of the precursor material 14 and the intermediate material30 (FIG. 2) with the process gas 62. That is, the process gas 62comprises higher concentrations of the reducing gas 64 and thecarbonizing gas 63 when it is initially introduced to the processchamber 34 and is thus likely to more readily react with the remainingor unreacted portion of the precursor material 14 and/or theintermediate material 30 at the far end of the process chamber 34.

[0043] The unreacted process gas 62 that flows upstream toward the entryof the process chamber 34 thus comprises a lower concentration of thecarbonizing gas 63 and the reducing gas 64. However, presumably a largersurface area of unreacted precursor material 14 is available at or nearthe entry of the process chamber 34. As such, smaller concentrations ofcarbonizing gas 63 and reducing gas 64 may be required to react with theprecursor material 14 at or near the entry of the process chamber 34. Inaddition, introducing the process gas 62 in such a manner may enhancethe efficiency with which the carbonizing gas 63 and the reducing gas 64is consumed by the reaction therebetween, for reasons similar to thosejust explained.

[0044] It is understood that in other embodiments of the invention theprocess gas 62 may be introduced in any other suitable manner. Forexample, the process gas 62 may be introduced through multiple injectionsites (not shown) along the length of the process chamber 34. Or forexample, and as explained above, the process gas 62 may be premixed andstored in its combined state in one or more gas cylinders forintroduction into the furnace 16. These are merely exemplaryembodiments, and still other embodiments are also contemplated as beingwithin the scope of the invention.

[0045] The process gas 62 may also be used to maintain the internal orreaction portion of the process chamber 34 at a substantially constantpositive pressure, as is desired according to preferred embodiments ofthe invention to exclude any oxygen from the process chamber 34 in caseof a leak. Indeed, according to one embodiment of the invention, theprocess chamber 34 is maintained at about 8.9 cm to 12.7 cm (3.5 in to 5in) of water pressure (gauge), and preferably at about 11.4 cm (4.5 in)of water pressure (gauge). The process chamber 34 may be maintained at aconstant pressure, according to one embodiment of the invention, byintroducing the process gas 62 at a predetermined rate, or pressure,into the process chamber 34, and discharging the unreacted process gas62 at a predetermined rate, or pressure, therefrom to establish thedesired equilibrium pressure within the process chamber 34.

[0046] Preferably, the process gas 62 (i.e., the unreacted carbonizinggas 63 and the unreacted reducing gas 64) is discharged from the processchamber 34 through a scrubber 66 at or near the entry of the processchamber 34 to maintain the process chamber 34 at a substantiallyconstant pressure. The scrubber 66 may comprise a dry pot 67, a wet pot68, and a flare 69. The dry pot 67 is preferably provided upstream ofthe wet pot 68 for collecting any dry material that may be dischargedfrom the process chamber 34 to minimize contamination of the wet pot 68.The process gas 62 is discharged through the dry pot 67 and into watercontained in the wet pot 68. The depth of the water that the process gas62 is discharged into within the wet pot 68 controls the pressure of theprocess chamber 34. Any excess gas may be burned at the flare 69.

[0047] Other embodiments for maintaining the process chamber 34 at asubstantially constant pressure are also contemplated as being withinthe scope of the invention. For example, a discharge aperture (notshown) may be formed within a wall 74 (FIG. 2) of the process chamber 34for discharging the unreacted process gas 62 from the process chamber 34to maintain the desired pressure therein. Or for example, one or morevalves (not shown) may be fitted into a wall 74 (FIG. 2) of the processchamber 34 for adjustably releasing or discharging the unreacted processgas 62 therefrom. Yet other embodiments for maintaining the pressurewithin the process chamber 34 are also contemplated as being within thescope of the invention.

[0048] The various components of apparatus 10, such as are shown in FIG.1 and described in the immediately preceding discussion, arecommercially available. For example, a Harper Rotating Tube Furnace(Model No. HOU-6D60-RTA-28-F), is commercially available from HarperInternational Corporation (Lancaster, N.Y.), and may be used accordingto the teachings of the invention, at least in part, to producemolybdenum carbide product 12.

[0049] The Harper Rotating Tube Furnace features a high-heat chamberwith a maximum temperature rating of 1450° C. A number of refractorydams divide the high-heat chamber into three independent temperaturecontrol zones. The three temperature control zones feature discretetemperature control using twenty-eight silicon-carbide electricalresistance heating elements. Thermocouplers are provided at the centerof each control zone along the centerline of the roof of the furnace.The temperature control zones are regulated by three Honeywell UDC3000Microprocessor Temperature Controllers, and by three Honeywell UDC2000Microprocessor Temperature Limiters, each commercially available fromHoneywell International, Inc. (Morristown, N.J.).

[0050] The Harper Rotating Tube Furnace also features a gas-tight, hightemperature alloy process chamber, having a maximum rating of 1100° C.The process chamber has a nominal internal diameter of 15.2 cm (6.0 in),nominal external ends diameter of 16.5 cm (6.5 in), and an overalllength of 305 cm (120 in). The process chamber extends in equal segments(each having a length of 50.8 cm (20 in)) through each of thetemperature control zones, leaving 152 cm (60 in) extending through thecooling zone.

[0051] The process chamber provided with the Harper Rotating TubeFurnace may be inclined within a range of 0 to 5°. In addition, theHarper Rotating Tube Furnace may be provided with a variable directcurrent (DC) drive with digital speed control for rotating the processchamber at rotational speeds of one to five revolutions per minute(rpm).

[0052] The Harper Rotating Tube Furnace also features a 316-liter,stainless steel, gas-tight with inert gas purge, discharge hopper. TheHarper Rotating Tube Furnace also features an atmosphere process gascontrol system for maintaining a constant pressure within the processchamber. In addition, a 45-kilowatt (kW) power supply may be provided,for heating the furnace and driving the process chamber. In addition,the Harper Rotating Tube Furnace may be fitted with a BrabenderLoss-In-Weight Feed System (Model No. H31-FW33/50), commerciallyavailable from C.W. Brabender Instruments, Inc. (South Hackensack,N.J.).

[0053] Although preferred embodiments of apparatus 10 are shown in FIG.1 and have been described above, it is understood that other embodimentsof apparatus 10 are also contemplated as being within the scope of theinvention. In addition, it is understood that apparatus 10 may compriseany suitable components from various manufacturers, and are not limitedto those provided herein. Indeed, where apparatus 10 is designed forlarge or industrial-scale production, the various components may bespecifically manufactured therefor, and the specifications will dependon various design considerations, such as but not limited to, the scalethereof.

Method for Producing Molybdenum Carbide

[0054] Having described apparatus 10, and preferred embodiments thereof,that may be used to produce molybdenum carbide product 12 according tothe invention, attention is now directed to embodiments of a method forproducing molybdenum carbide product 12. As an overview, and still withreference to FIG. 1, the precursor material 14 is preferably introducedinto the furnace 16 and moved through the heating zones 20, 21, and 22,and the cooling zone 23 thereof. The process gas 62 is preferablyintroduced into the furnace 16 for reaction with the precursor material14 and the intermediate material 30. The precursor material 14 and theintermediate material 30 react with the process gas 62 therein toproduce molybdenum carbide product 12 (i.e., MoC and/or Mo₂C), asdiscussed in more detail below with respect to preferred embodiments ofthe method.

[0055] According to preferred embodiments, the precursor material 14comprises nano-particles of molybdic oxide (MoO₃). The nano-particles ofmolybdic oxide preferably have a typical surface area to mass ratio ofabout 25 to 35 m²/g. These nano-particles of molybdic oxide may beproduced according to embodiments of the invention disclosed in co-ownedU.S. Pat. No. 6,468,497 issued on Oct. 22, 2002 for “METHOD FORPRODUCING NANO-PARTICLES OF MOLYBDENUM OXIDE” of Khan, et al., which isincorporated herein for all that it discloses. The nano-particles ofmolybdic oxide are produced by, and are commercially available from theClimax Molybdenum Company (Fort Madison, Iowa).

[0056] According to other embodiments of the invention, however, it isunderstood that the precursor material 14 may comprise any suitablegrade or form of molybdic oxide (MoO₃). For example, the precursormaterial 14 may range in size from 0.5 to 80 m²/g. In yet otherembodiments of the invention, the precursor material 14 may compriseother materials, such as ammonium molybdate, hydrogen-based molybdates,etc. Selection of the precursor material 14 may depend on various designconsiderations, including but not limited to, the desiredcharacteristics of the molybdenum carbide product 12 (e.g., surface areato mass ratio, size, purity, etc.).

[0057] In general, the surface area to mass ratio of the molybdenumcarbide product 12 is proportionate to the surface area to mass ratio ofthe precursor material 14. When molybdic oxide precursor material isused according to the teachings of the invention, the surface area tomass ratio of the molybdenum carbide product 12 typically ranges from 5to 11 m²/g.

[0058] Turning now to FIG. 2, the process chamber 34 (walls 74 thereofare shown) is illustrated in three cross-sectional portions of theprocess chamber 34. Each cross-sectional portion shown in FIG. 2 istaken respectively from each of the three heating zones 20, 21, and 22of the furnace 16. According to preferred embodiments of the method, theprecursor material 14 is introduced into the process chamber 34, andmoves through each of the three heating zones 20, 21, and 22 of thefurnace 16 (i.e., Heating Zone 1, Heating Zone 2, and Heating Zone 3, inFIG. 2). The process chamber 34 may be rotating and/or inclined tofacilitate movement and mixing of the precursor material 14 therein, asdescribed in more detail above with respect to embodiments of apparatus10. In addition, the process gas 62 is also introduced into the processchamber 34. Preferably, the process gas 62 flows through the processchamber 34 in a direction 28 that is opposite or counter-current to thedirection 26 that the precursor material 14 is moving through theprocess chamber 34, such as may be accomplished according to theembodiments of apparatus 10 discussed in more detail above.

[0059] As the precursor material 14 moves through the heating zones 20,21, and 22, it is mixed with the process gas 62 and reacts therewith toform intermediate product 30, and then the molybdenum carbide product12. The reaction is illustrated by arrows 70, 71, and 72 in therespective heating zones 20 (Heating Zone 1), 21 (Heating Zone 2), and22 (Heating Zone 3) of FIG. 2. More particularly, the reactions may bedescribed as solid molybdic oxide (MoO₃) being reduced by the reducinggas 64 (e.g., hydrogen gas), and carbonized by the carbonizing gas 63(e.g., carbon monoxide gas).

[0060] The temperature in the first heating zone 20 is preferablymaintained below the vaporization temperature of the precursor material14, and that of any intermediate material 30 that is formed in the firstheating zone 20 (Heating Zone 1), relative to the pressure within theprocess chamber 34. Overheating the precursor material 14 and/or theintermediate material 30 may cause a reaction only on the surfacethereof. The resulting surface reaction may seal unreacted precursormaterial 14 and/or intermediate material 30 therein. Thus, longerprocessing times and/or higher processing temperatures may be requiredto convert these “beads” to molybdenum carbide product 12, thus reducingthe efficiency and increasing the cost of production.

[0061] The temperature of the first heating zone 20 is preferablymaintained at a lower temperature than the other two heating zones 21,and 22 because the reaction between the precursor material 14 and theprocess gas 62 in the first heating zone 20 (Heating Zone 1) is anexothermic reaction. That is, heat is released during the reaction inthe first heating zone 20.

[0062] The reaction between the intermediate material 30 and the processgas 62 in the third heating zone 22 (Heating Zone 3) is an endothermicreaction. That is, heat is consumed during this reaction. Therefore, theenergy input of the third heating zone 22 is preferably adjustedaccordingly to provide the additional heat required by the endothermicreaction in the third heating zone 22.

[0063] When the molybdenum carbide 12 produced by the reactionsdescribed above is immediately introduced to an atmospheric environmentwhile still hot (e.g., upon exiting the third heating zone 22), it mayreact with one or more constituents of the atmosphere. Therefore, themolybdenum carbide product 12 is preferably moved through a cooling zone23 in a reducing environment (e.g., the process gas 62 flows through thecooling zone 23). Accordingly, the hot molybdenum carbide product 12 maybe cooled for handling purposes before being exposed to the atmosphere.

[0064] The reactions shown in each of the heating zones 20, 21, and 22in FIG. 2 are merely illustrative of the process of the invention. Aswill be readily apparent to one skilled in the art, it is understoodthat one or more reactions may occur in each of the three heating zones20, 21, and 22, as illustrated by arrows 70, 71, and 72. Indeed, somemolybdenum carbide product 12 may be formed in the first heating zone 20and/or the second heating zone 21. Likewise, some unreacted precursormaterial 14 may be introduced into the second heating zone 21 and/or thethird heating zone 22. In addition, some reactions may still occur evenin the cooling zone 23.

[0065] Also as will be readily apparent to one skilled in the art, anyunreacted process gas 62 is discharged in the effluent. Likewise, wherethe reducing agent combines with oxygen stripped from the molybdic oxideand/or combines with the unreacted carbonizing gas, these may also bereleased in the effluent.

[0066] Having discussed the reactions in the furnace 16 illustrated inFIG. 2, it should be noted that optimum conversion of the precursormaterial 14 to the molybdenum carbide product 12 were observed to occurwhen the process parameters were set to values in the ranges shown inTable 1. TABLE 1 PARAMETER SETTING Process Chamber Incline 0.15° to 1.0°Process Chamber Rotation Rate 15 to 35 seconds per revolutionTemperature (for MoC) Zone 1 540° C. to 590° C. Zone 2 and Zone 3 820°C. to 940° C. Zone 3 880° C. to 950° C. Temperature (for Mo₂C) Zone 1540° C. to 590° C. Zone 2 and Zone 3 760° C. to 820° C. Zone 3 980° C.to 1040° C. Reducing Gas Flow Rate 15 to 50 cubic feet per hourCarbonizing Gas Flow Rate 15 to 50 cubic feet per hour

[0067] The gas flow rates of the reducing gas and of the carbonizing gasare preferably in equal proportion to one another, or within about 5cubic feet per hour of equal flow rates.

[0068] It is understood that molybdenum carbide product 12 may also beproduced when the process parameters are adjusted outside of the rangesgiven above in Table 1, as may be readily determined by one skilled inthe art based on the teachings of the invention.

[0069] According to preferred embodiments of the invention, it is notnecessary to screen the molybdenum carbide product 12 to removeprecursor material 14, intermediate material 30, and/or othercontaminating material (not shown) from the product. That is,preferably, 100% of the precursor material 14 is fully converted to puremolybdenum carbide product 12. However, according to embodiments of theinvention, the molybdenum carbide product 12 may be screened to removeoversize particles from the product that may have agglomerated duringthe process. Whether the molybdenum carbide product 12 is screened willdepend on design considerations such as, but not limited to, theultimate use for the molybdenum carbide product 12, the purity and/orparticle size of the precursor material 14, etc.

[0070] An embodiment of a method for producing molybdenum carbide 12according to the teachings of the invention is illustrated as steps inthe flow chart shown in FIG. 3. In step 80, the precursor material 14may be introduced into the reaction chamber (e.g., process chamber 34 offurnace 16). As discussed above, the precursor material 14 is preferablyintroduced into the furnace 16 by feeding it into the process chamber 34extending through the furnace 16. In step 82, the process gas 62 may beintroduced into the reaction chamber (e.g., process chamber 34 offurnace 16). Again, as discussed above, the process gas 62 is preferablyintroduced into the process chamber 34 and preferably flows therethroughin a direction 28 that is opposite or counter-current to the direction26 that the precursor material 14 is moving through the furnace 16. Instep 84, the three heating zones of the reaction chamber are heated andthe precursor material moved through the heating zones 20, 21, and 22.The temperature is increased at least once by at least 100° C. (e.g., asthe material moves through the heating zones 20, 21, and 22).Accordingly, the precursor material 14 is converted to molybdenumcarbide 12, as illustrated by step 86 and described in more detail abovewith respect to FIG. 2.

[0071] It is understood that the steps shown and described with respectto FIG. 3 are merely illustrative of an embodiment of the method forproducing molybdenum carbide 12. It is expected that yet otherembodiments of the method for producing molybdenum carbide product thatare within the scope of the invention will become readily apparent toone skilled in the art based on the teachings of the invention.

EXAMPLES

[0072] In the following examples, the precursor material comprisednano-particles of molybdic oxide (MoO₃) having a typical size of about25 to 35 m²/g. Such nano-particles of molybdic oxide may be producedaccording to embodiments of the invention disclosed in co-owned U.S.Patent Application No. 6,468,497 for “METHOD FOR PRODUCINGNANO-PARTICLES OF MOLYBDENUM OXIDE.” The nano-particles of molybdicoxide used as precursor material in this example are produced by and arecommercially available from the Climax Molybdenum Company (Fort Madison,Iowa).

[0073] The following equipment was used for this example: a BrabenderLoss-In-Weight Feed System (Model No. H31-FW33/50), commerciallyavailable from C.W. Brabender Instruments, Inc. (South Hackensack,N.J.); and a Harper Rotating Tube Furnace (Model No. HOU-6D60-RTA-28-F),commercially available from Harper International Corporation (Lancaster,N.Y.). The Harper Rotating Tube Furnace comprised three independentlycontrolled 50.8 cm (20 in) long heating zones with a 305 cm (120 in) HTalloy tube extending through each of the heating zones thereof.Accordingly, a total of 152 cm (60 in) of heating and 152 cm (60 in) ofcooling were provided in this example.

[0074] The precursor material was fed at a rate of about five to sevengrams per minute using the Brabender Loss-In-Weight Feed System into theHT alloy tube of the Harper Rotating Tube Furnace. The carbonizing gasand the reducing gas were each introduced through the HT alloy tube at arate of 30 cubic feet per hour in a direction opposite orcounter-current to the direction that the precursor material was movingthrough the HT alloy tube. In this example, the process gas comprisedcarbon monoxide as the carbonizing gas and hydrogen gas as the reducinggas. Nitrogen gas was used to purge the process chamber. Alternatively,argon gas was also used to purge the process chamber. The discharge gaswas bubbled through a water scrubber to maintain the interior of thefurnace at approximately 11.4 cm (4.5 in) of water pressure (gauge).

Example 1 MoC Production

[0075] In Example 1, the HT alloy tube was rotated at about 20 secondsper revolution, and inclined about 0.25° to facilitate movement of theprecursor material through the Harper Rotating Tube Furnace, and tofacilitate mixing of the precursor material with a process gas. Optimumconversion of the precursor material to molybdenum carbide (MoC) productin one pass through the furnace occurred when the temperature of thefirst heating zone (Heating Zone 1) was set to about 555° C., and thetemperature of the second and third heating zones (Heating Zone 2 andHeating Zone 3) were each set to about 900° C. Accordingly, thereactants were heated to 555° C. for approximately one-third of theprocessing time (i.e., based on one-third of the overall process chamberlength) and heated to 900° C. for approximately two-thirds of theprocessing time (i.e., based on two-thirds of the overall processchamber length).

[0076] Molybdenum carbide (MoC) produced according to this example ischaracterized by a surface area to mass ratio of 11.5 to 14 m²/g.

Example 2 Mo₂C Production

[0077] In Example 2, the HT alloy tube was rotated at about 28 secondsper revolution, and inclined about 0.5° to facilitate movement of theprecursor material through the Harper Rotating Tube Furnace, and tofacilitate mixing of the precursor material with a process gas. Optimumconversion of the precursor material to molybdenum carbide (Mo₂C)product in one pass through the furnace occurred when the temperature ofthe first heating zone (Heating Zone 1) was set to about 555° C., thetemperature of the second heating zone (Heating Zone 2) was set to about800° C., and the temperature of the third heating zone (Heating Zone 3)was set to about 1000° C.

[0078] Molybdenum carbide (Mo₂C) produced according to this example ischaracterized by a surface area to mass ratio of 5 to 11 m²/g.

[0079] It is readily apparent that apparatus and methods for productionof molybdenum carbide (MoC and Mo₂C) discussed herein may be used toproduce molybdenum carbide in a continuous, single stage manner.Consequently, the claimed invention represents an important developmentin molybdenum carbide technology. Having herein set forth various andpreferred embodiments of the invention, it is expected that suitablemodifications will be made thereto which will nonetheless remain withinthe scope of the invention. Accordingly, the invention should not beregarded as limited to the embodiments shown and described herein, andit is intended that the appended claims be construed to include yetother embodiments of the invention, except insofar as limited by theprior art.

What is claimed is:
 1. MoC produced by heating a precursor material in afirst heating zone to a first temperature in the presence of a reducinggas and a carbonizing gas and moving the precursor material to a secondheating zone that is heated to a second temperature that is at least100° C. hotter than the first heating zone.
 2. Mo₂C produced by heatinga precursor material in a first heating zone to a first temperature inthe presence of a reducing gas and a carbonizing gas and moving theprecursor material to a second heating zone that is heated to a secondtemperature that is at least 100° C. hotter than the first heating zone.